Thickening agent for alkaline battery, and alkaline battery

Abstract

Provided are a thickening agent for an alkaline battery, which can satisfactorily retain long-term discharge characteristics (discharge quantity and discharge time) and provide excellent impact resistance, and an alkaline battery used therewith. In the invention, the thickening agent for an alkaline battery comprises (A) a crosslinked polymer comprising, as essential constituent units, (a1) a water-soluble vinyl monomer and/or (a2) a vinyl monomer being converted into (a1) by hydrolysis, (b) a hydrolyzable crosslinking agent undergoing alkaline hydrolysis, and (c) a non-hydrolyzable crosslinking agent not undergoing alkaline hydrolysis, wherein (b) and (c) each has a content of 0.05% to 1% by weight based on the weight of (A), and satisfies Requirements (1) and (2) described below: Requirement (1): the weight ratio (b)/(c) between (b) and (c) is from 1.0 to 5.0; Requirement (2): a specific solution (S1) has a viscosity of 25 to 100 Pa·s at 25° C.

The invention claimed is: 
     
       1. A thickening agent for an alkaline battery, which comprises (A) a crosslinked polymer comprising, as essential constituent units, (a1) a water-soluble vinyl monomer and/or (a2) a vinyl monomer being converted into (a1) by hydrolysis, (b) a hydrolyzable crosslinking agent undergoing alkaline hydrolysis, and (c) a non-hydrolyzable crosslinking agent not undergoing alkaline hydrolysis, wherein (b) and (c) each has a content of 0.05% to 1% by weight based on the weight of (A), and which satisfies Requirements (1) to (3) described below:
 Requirement (1): the weight ratio (b)/(c) between (b) and (c) is from 1.0 to 5.0; 
 Requirement (2): the solution (S1) described below has a viscosity of 25 to 100 Pa·s at 25° C.; 
 Solution (S1): a solution obtained by mixing 98 parts by weight of an aqueous 40% by weight potassium hydroxide solution and 2 parts by weight of the thickening agent for an alkaline battery and stirring the mixture to form a uniform solution and allowing the solution to stand at 25° C. for 24 hours, 
 Requirement (3): the solution (S2) described below shows a syneresis rate of 6.5% by weight or less; 
 Solution (S2): a solution obtained by mixing 100 parts by weight of an aqueous 35% by weight potassium hydroxide solution, 2 parts by weight of the thickening agent for an alkaline battery, and 200 parts by weight of a zinc powder and stirring the mixture to form a uniform solution and allowing the solution to stand at 25° C. for 24 hours. 
 
     
     
       2. The thickening agent for an alkaline battery according to  claim 1 , wherein (b) is a compound having an ester bond and/or an amide bond or a compound capable of forming an ester bond and/or an amide bond. 
     
     
       3. The thickening agent for an alkaline battery according to  claim 1 , wherein (b) is N,N′-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, or ethylene glycol diglycidyl ether. 
     
     
       4. The thickening agent for an alkaline battery according to  claim 1 , wherein (c) is a compound having two to ten allyl groups and one to five hydroxyl groups. 
     
     
       5. The thickening agent for an alkaline battery according to  claim 1 , wherein (c) is trimethylolpropane diallyl ether or pentaerythritol diallyl ether. 
     
     
       6. The thickening agent for an alkaline battery according to  claim 1 , wherein the crosslinked polymer (A) is a product obtained by solution polymerization or reverse phase suspension polymerization. 
     
     
       7. An alkaline battery, comprising the thickening agent for an alkaline battery according to  claim 1  and a zinc powder. 
     
     
       8. The thickening agent for an alkaline battery according to  claim 1 , wherein
 Requirement (1): the weight ratio (b)/(c) between (b) and (c) is from 1.3 to 4.5; 
 Requirement (2): the solution (S1) described below has a viscosity of 27 to 60 Pa·s at 25° C.; 
 Requirement (3): the solution (S2) shows a syneresis rate of 2.4% to 6.5% by weight or less.